1. Field of the Invention
The present invention relates to a valve timing control device for modifying the. opening and closing timing of the intake and exhaust valves in an internal-combustion engine (hereafter, referred as an engine) according to any operating condition.
2. Description of the Prior Art
Conventional valve timing control devices having various kinds of construction are provided as disclosed in JP-A-1998/159519 and JP-A-1998/159520, for example.
FIG. 1 is a lateral cross-sectional view of an internal construction of a conventional vane-type valve timing control device. FIG. 2 is a longitudinal cross sectional view taken along lines Axe2x80x94A of FIG.1. FIG. 3A is an enlarged longitudinal cross sectional view of a release valve in the conventional valve timing control device shown in FIG. 1 and FIG. 2. FIG. 3B is an enlarged lateral cross sectional view of the state of the release valve on application of advance hydraulic pressure. FIG. 3C. is an enlarged lateral cross sectional view of the state of the release valve on application of retardation hydraulic pressure. In the drawings, reference numeral 1 denotes a pulley connected to a crankshaft (not shown) of the engine to rotate in conjunction with the crankshaft (not shown) through chains (not shown). 2 denotes a housing fixedly provided with the pulley 1 and having a bearing 2a used between the housing 2 and an intake camshaft or an exhaust camshaft (hereafter, referred as a camshaft). 4 denotes a case having a plurality of shoes 4a projected from an inner peripheral portion of the case 1 to constitute a plurality of hydraulic pressure chambers between the shoes 4a. 5 denotes a cover for closing the hydraulic pressure chambers of the case 4. The housing 2, the case 4 and the cover 5 are integrated by a threaded member 6 such as bolts and so on. Here, the pulley 1, the housing 2, the case 4 and the cover 5 constitute a first rotor.
A rotor (second rotor) 9 is integrally locked on one end 3a of the camshaft 3 through a washer 7 by a threaded member 8 such as bolts and so, on. The rotor 9 is rotatably arranged within the first rotor. A plurality of vanes 9a is arranged an outer peripheral portion of the rotor 9 to divide the plurality of hydraulic pressure chambers into advance side hydraulic pressure chambers 10 and retardation side hydraulic pressure chambers 11. A first oil path 12 and a second oil path 13 are arranged within the camshaft 3. The first oil path 12 performs supplies of hydraulic pressure to and. discharges thereof from the advance side hydraulic pressure chamber 10. The second oil path 13 supplies hydraulic pressure to and discharges hydraulic pressure from the retardation.side hydraulic pressure chamber 11. Further, seal members i4 are arranged on both front ends of the shoes 4a of the case 4 and the vanes 9a of the rotor 9, respectively. The each seal member 14 includes a seal 14a and a plate spring 14b to prevent leakage of oil between the both hydraulic pressure chambers 10 and 11.
A lock pin 15 having a substantially cylindrical shape is arranged on the housing 2 constituting the first rotor, and controls the relative rotation of the first and second rotors to prevent the following occurrence of beat noise (abnormal noise). Since a hydraulic pressure within the valve timing control device is reduced on starting the engine, the rotor 9 vibrates in the rotational direction as a result of a cam load applied to a cam (not shown) integrated with the camshaft 3 and thus the first and second rotors undergo repetitive contact and separation as a result of the vibration. Therefore, the lock pin. 15 can engage in an engagement hole as will be explained hereafter due to being biased by a biasing member 17 such as coil spring and so on, the biasing member 17 being arranged between a rear wall within a backward pressure chamber 16 and the lock pin 15. The lock pin 15 includes a small radius part 15a inserted in the engagement hole, a large radius part 15b having an outer diameter substantial equal to an inner diameter of the backward pressure chamber 16, and a hole 15c having a bottom therein. The hole 15c is formed in the large radius part 15b and supports one end of the biasing member 17. A discharge hole 18 is formed in the backward pressure chamber 16, the discharge hole 18 of discharging a backward pressure of the lock pin 15. On the other hand, the engagement hole 19 for allowing insertion of the lock pin 15.is formed in the vane 9a of the rotor 9 acting as the second rotor. The engagement hole 19 communicates with a release valve 21 through an oil hydraulic supply path 20 of supplying hydraulic pressure to release the lock pin 15. As shown in FIG. 3A, FIG. 3B and FIG. 3C, the release valve 21 includes a valve chamber 21a having an oval shape, a slide plate 21b having a circular shape in cross section, and a perforation hole 21c having an oval shape in cross section. The slide plate 21b is movable in a long radius direction in the valve chamber 21a. The perforation hole 21c is formed at a bottom of the valve chamber 21a, and communicates with the oil hydraulic supply path 20. As shown in FIG. 1, FIG. 3A, FIG. 3B and FIG. 3C, an advance side pressure partition path 22 communicates with the advance side hydraulic pressure chamber 10 and a retardation side pressure partition path 23 communicates with the retardation side hydraulic pressure chamber 11. These paths 22 and 23 are connected to the valve chamber 21a of the release valve 21. With the release valve 21, when the pressure of the advance side hydraulic pressure chamber 10 is higher than that of the retardation side hydraulic pressure chamber 11, as shown in FIG. 3B, the slide plate 21b moves toward the retardation side in the valve chamber 21a. Thus, the slide plate 21b closes the retardation side pressure partition path 23, and communicates the advance side pressure partition path 22 to the oil hydraulic supply path 20 through the perforation hole 21c to supply the hydraulic pressure of the advance side hydraulic pressure chamber 10 thereto. On the other hand, when pressure of the retardation side hydraulic pressure chamber 11 is higher than that of the advance side hydraulic pressure chamber 10, as shown in FIG. 3A and FIG. 3C, the slide plate 21b moves toward. the advance side in the valve chamber 21a. Thus, the slide plate 21b closes the advance side pressure partition path 22, and communicates the retardation side pressure partition path 23 to the oil hydraulic supply path 20 through the perforation hole 21c to supply the hydraulic pressure of the retardation side hydraulic pressure chamber 11 thereto.
Next, a release operation will be described.
When the lock is released, hydraulic pressure from an oil pump (not shown) is supplied to the engagement hole 19 through the advance side hydraulic pressure chamber 10 or the retardation side hydraulic pressure chamber 11, the release valve 21 and the oil hydraulic supply path 20. Thus, the lock pin 15 is moved backward in the backward pressure chamber 16 against the biasing force of the biasing member 17. Here, the backward pressure of the lock pin 15 is discharged through the discharge hole 18 to the outside of the valve timing control device. With the discharge of the backward pressure, the area subjected to hydraulic pressure is constant from the locked state to the released state. When the small radius part 15a of the lock pin 15 is disconnected from the engagement hole 19 to be held in the backward pressure chamber 16, the lock pin 15 is released to allow free rotation between the first and second rotors.
Incidentally, when the engine is stopped, oil in the advance side hydraulic pressure chamber 10 and the retardation side hydraulic pressure chamber 11 moves downwardly to an oil-pan (not shown) through the first and second oil path 12 and 13 and so on. Therefore, air builds up in pipe arrangement such as the respective hydraulic pressure chambers and the respective oil paths. When the engine is restarted in this state, the hydraulic pressure is increased due to the oil pump (not shown) and air accumulated in the pipe arrangement is simultaneously discharged at once. Thus, the air-mixing oil is applied in the valve timing control device to release instantly the lock pin 15 from the engagement hole 19.
However, the following problems result from the above structure for a conventional valve timing control device.
When the air-mixing oil releases the lock on starting the engine, the hydraulic pressure in the advance side hydraulic pressure chamber 10 and the retardation side hydraulic pressure chamber 11 cannot absorb the cam load described above. Since the first and second rotors repeat contact and separation there-between, it cannot prevent the occurrence of beat noise (abnormal noise).
Accordingly, it is an object of the present invention to provide a valve timing control device, which prevents the occurrence of beat noise (abnormal noise) in release operation occurred by the air-mixing oil on starting the engine.
In order to achieve the object of the present invention, a valve timing control device comprises a first rotor rotating in synchronization with a crankshaft of an internal-combustion engine; a second rotor fixed on an end of an intake camshaft or an exhaust camshaft of the internal-combustion engine and rotatably arranged in the first rotor; a lock member locking the first and second rotors at a required angle which the second rotor forms with the first rotor; a backward pressure chamber arranged at any one of the first and second rotors, accommodating the lock member and a biasing member biasing the lock member, and having a discharge hole of discharging backward pressure of the lock member; and an engagement hole arranged in the other, allowing insertion of the lock member, and having an oil hydraulic supply path supplying hydraulic pressure to release the lock member, wherein releasing hydraulic pressure characteristics is provided with a hysteresis characterized in that releasing hydraulic pressure is larger than holding-releasing hydraulic pressure. Thus, when hydraulic pressure rises on starting the engine, the lock member is not quickly released, and is released after applying hydraulic pressure which controls the valve timing control device. Therefore, it can prevent the occurrence of beat noise (abnormal noise).
The valve timing control device may comprise a purge valve mechanism arranged within the lock member, and discharging the releasing hydraulic pressure to the outside, wherein the hysteresis is constituted by the purge valve mechanism. Thus, a part of hydraulic pressure applied to the engagement hole on releasing the lock member is discharged through the purge valve mechanism to outside the device to reduce hydraulic pressure acting the sliding of the lock member. Therefore, it can delay a release operation.
The purge valve mechanism may be a slide valve mechanism. Thus, a part of hydraulic pressure applied to the engagement hole on releasing the lock member is discharged through the slide valve mechanism to outside the device to reduce hydraulic pressure acting the sliding of the lock member. Therefore, it can delay a release operation.
The purge valve mechanism may be a check valve mechanism. Thus, a part of hydraulic pressure applied to the engagement hole on releasing the lock member is discharged through the check valve mechanism to outside the device to reduce hydraulic pressure acting the sliding of the lock member. Therefore, it can delay a release operation.
The purge valve mechanism may be a lead valve mechanism. Thus, a part of hydraulic pressure applied to the engagement hole on releasing the lock member is discharged through the lead valve mechanism to outside the device to reduce hydraulic pressure acting the sliding of the lock member. Therefore, it can delay a release operation.
The hysteresis may be constituted by a difference in the flow rate between pressurized fluids which are set by elasticity of the purge valve mechanism or a support member of the purge valve mechanism. Thus, limited oil flow relating to the release of the lock can delay a release operation.
The valve timing control device may comprise a first rotor rotating in synchronization with a crankshaft of an internal-combustion engine; a second rotor fixed.on an end of an intake camshaft or an exhaust camshaft of the internal-combustion engine and rotatably arranged in the first rotor; a lock member locking the first and second rotors at a required angle which the second rotor forms with the. first rotor; a backward pressure chamber arranged at any one of the first and second rotors, accommodating the lock member and a biasing member biasing the lock member, and having a discharge hole of discharging backward pressure of the lock member; an engagement hole arranged in the other, allowing insertion of the lock member, and having an oil hydraulic supply path supplying hydraulic pressure to release the lock member; and a release valve having an advance side pressure partition path communicating an advance side hydraulic pressure chamber and a retardation side pressure partition path communicating a retardation side hydraulic pressure chamber to selectively supply the highest hydraulic pressure in the both chambers to the oil hydraulic supply path, wherein releasing hydraulic pressure characteristics are provided with a hysteresis characterized in that releasing hydraulic pressure is larger than holding-releasing hydraulic pressure, the hysteresis is constituted by a difference in the flow rate between pressurized fluids from the advance side hydraulic pressure chamber and the retardation side hydraulic pressure chamber. Thus, limited oil flow relating to the release of the lock can delay a release operation.
The oil hydraulic supply path communicating the release valve may be divided into an advance side oil hydraulic supply path and a retardation side oil hydraulic supply path. The difference in the flow rate between pressurized fluids may be set by an opening area difference between the advance and retardation oil hydraulic supply paths. Thus, limited oil flow relating to the release of the lock can delay a release operation.
The difference in the flow rate between pressurized fluids may be set by an opening area difference between an advance side pressure partition path and a retardation side pressure partition path, the respective paths communicating with the release valve. Thus, limited oil flow relating to the release of the lock can delay a release operation.
The difference in the flow rate between pressurized fluids may be set by a difference in the length between an advance side pressure partition path and a retardation side pressure partition path, the respective paths communicating with the release valve. Thus, limited oil flow relating to the release of the lock can delay a release operation.
The difference in the flow rate between pressurized fluids may be set by a bending difference between an advance side pressure partition path and a retardation side pressure partition path, the respective paths communicating the release valve. Thus, limited oil flow relating to the release of the lock can delay a release operation.